Technical Abstract:
Tomato fruits were engineered to accumulate polyamines, spermidine and spermine, during ripening by genetic introduction of yeast S-adenosylmethionine decarboxylase gene fused with the ripening-and ethylene-inducible E-8 promoter. Beneficial attributes of the transgenic fruit include longer vine and shelf life, robustness and a 3-fold increase in the lycopene content. Surprisingly, these fruit consistently produced more ethylene than the non-transformed or azygous fruit. This in vivo observation is in contrast to our previous in vitro studies where incubation of tomato fruit slices with mM concentrations of spermidine and spermine inhibited accumulation of ACC synthase transcripts. We are investigating the molecular basis for the in vivo stimulation of ethylene in the transgenic fruit. We tested whether the E- 8 promoter sequences in the gene construct co-suppressed the endogenous E8 gene, which is an ethylene biosynthesis suppressor. We also analyzed accumulation of transcripts for ACC synthase, ACC oxidase, etr3, actin, E-8, and rDNA in transgenic and non-transgenic fruits. These data will be presented and discussed in relation to metabolic interactions between polyamines and ethylene in climacteric fruits.